[PRICE MISMATCHED!] - Rest API Companion vs IG Web Platform

[insignificant]

Hi IG Support,

I'm currently developing a monitoring tools for the price using REST API. 

I have couple of questions that really confused me in constructing the formula/algorithm:

1. I have been comparing price in the IG Web Platform and Android Platform versus the REST API Companion. I found some inconsistencies, for example at some points in Web/Android platform to calculate the Mid HIGHEST price, the formula is as follow: ROUND_DOWN((Bid + Ask)/2); However, on the same timeframe at some points the Mid LOWEST price formula is as follow: ROUND_UP((Bid + Ask)/2). Please see my attached screenshot for more details. This brought me to a question as how to calculate the Mid value of a candle in the Web/Android Platform, let's say (Bid + Ask)/2 = 107.01235, so should it get rounded up becoming 107.013 or rounded down becoming 107.012?
2. Issue number 1 somehow screws my Stochastic Oscillator calculation due to inconsistencies and differences in couple of N candles. Does IG have an API to call the Stoch value at some point of time?
3. Did I calculate point 1 above incorrectly? What's the correct formula to get the accurate price at certain point? I was using the GET/prices - is that correct? Is my method correct?

Please see my screenshot for more detailed information 🙏

Thank you!